1,328 research outputs found
Alternative symplectic structures for SO(3,1) and SO(4) four-dimensional BF theories
The most general action, quadratic in the B fields as well as in the
curvature F, having SO(3,1) or SO(4) as the internal gauge group for a
four-dimensional BF theory is presented and its symplectic geometry is
displayed. It is shown that the space of solutions to the equations of motion
for the BF theory can be endowed with symplectic structures alternative to the
usual one. The analysis also includes topological terms and cosmological
constant. The implications of this fact for gravity are briefly discussed.Comment: 13 pages, LaTeX file, no figure
Feedback-limited Accretion: Luminous Signatures from Growing Planets
Planets form in discs of gas and dust around stars, and keep growing by
accretion of disc material while available. Massive planets clear a gap in that
protoplanetary disc, but still accrete through spiral wakes. On its way to the
planet, the gas will settle on a \emph{circumplanetary} disc around the planet
and slowly accrete on to it. The energy of the accreted gas will be released,
heating the planet surroundings in a feedback process. For high enough
accretion rates the planet should be detectable at infrared wavelengths. We aim
to find whether detectable planet luminosities, , can occur when considering that the planet luminosity is
coupled to the accretion, and also to study which other effects has the
feedback on the dynamics of the circumplanetary and the gap regions. We model a
planet with mass ratio , orbiting at 10 AU from a solar mass star,
using a modified version of the 2D code FARGO-AD, which includes a prescription
for the accretion and feedback luminosity of the planet. We find that the
planetary feedback is able to partially deplete the circumplanetary disc, and
to reduce the accretion rate onto the planet. However, detectable luminosities
of are still produced. The
feedback also contributes to partially refilling the gap, to heat up the
coorbital region, and to perturb the orbital velocity of the gas.Comment: Submitted to MNRA
Lorentz-covariant Hamiltonian analysis of BF gravity with the Immirzi parameter
We perform the Lorentz-covariant Hamiltonian analysis of two Lagrangian
action principles that describe general relativity as a constrained BF theory
and that include the Immirzi parameter. The relation between these two
Lagrangian actions has been already studied through a map among the fields
involved. The main difference between these is the way the Immirzi parameter is
included, since in one of them the Immirzi parameter is included explicitly in
the BF terms, whereas in the other (the CMPR action) it is in the constraint on
the B fields. In this work we continue the analysis of their relationship but
at the Hamiltonian level. Particularly, we are interested in seeing how the
above difference appears in the constraint structure of both action principles.
We find that they both possess the same number of first-class and second-class
constraints and satisfy a very similar (off-shell) Poisson-bracket algebra on
account of the type of canonical variables employed. The two algebras can be
transformed into each other by making a suitable change of variablesComment: LaTeX file, no figure
Linear constraints from generally covariant systems with quadratic constraints
How to make compatible both boundary and gauge conditions for generally
covariant theories using the gauge symmetry generated by first class
constraints is studied. This approach employs finite gauge transformations in
contrast with previous works which use infinitesimal ones. Two kinds of
variational principles are taken into account; the first one features
non-gauge-invariant actions whereas the second includes fully gauge-invariant
actions. Furthermore, it is shown that it is possible to rewrite fully
gauge-invariant actions featuring first class constraints quadratic in the
momenta into first class constraints linear in the momenta (and homogeneous in
some cases) due to the full gauge invariance of their actions. This shows that
the gauge symmetry present in generally covariant theories having first class
constraints quadratic in the momenta is not of a different kind with respect to
the one of theories with first class constraints linear in the momenta if fully
gauge-invariant actions are taken into account for the former theories. These
ideas are implemented for the parametrized relativistic free particle,
parametrized harmonic oscillator, and the SL(2,R) model.Comment: Latex file, revtex4, 18 pages, no figures. This version includes the
corrections to many misprints of v1 and also the ones of the published
version. The conceptual and technical parts of the paper are not altere
Real sector of the nonminimally coupled scalar field to self-dual gravity
A scalar field nonminimally coupled to gravity is studied in the canonical
framework, using self-dual variables. The corresponding constraints are first
class and polynomial. To identify the real sector of the theory, reality
conditions are implemented as second class constraints, leading to three real
configurational degrees of freedom per space point. Nevertheless, this
realization makes non-polynomial some of the constraints. The original complex
symplectic structure reduces to the expected real one, by using the appropriate
Dirac brackets. For the sake of preserving the simplicity of the constraints,
an alternative method preventing the use of Dirac brackets, is discussed. It
consists of converting all second class constraints into first class by adding
extra variables. This strategy is implemented for the pure gravity case.Comment: Latex file, 22 pages, no figure
Relational evolution of the degrees of freedom of generally covariant quantum theories
We study the classical and quantum dynamics of generally covariant theories
with vanishing a Hamiltonian and with a finite number of degrees of freedom. In
particular, the geometric meaning of the full solution of the relational
evolution of the degrees of freedom is displayed, which means the determination
of the total number of evolving constants of motion required. Also a method to
find evolving constants is proposed. The generalized Heinsenberg picture needs
M time variables, as opposed to the Heisenberg picture of standard quantum
mechanics where one time variable t is enough. As an application, we study the
parameterized harmonic oscillator and the SL(2,R) model with one physical
degree of freedom that mimics the constraint structure of general relativity
where a Schrodinger equation emerges in its quantum dynamics.Comment: 25 pages, no figures, Latex file. Revised versio
Estimating Venezuelas Latent Inflation
Percent variation of the consumer price index (CPI) is the inflation indicator most widely used. This indicator, however, has some drawbacks. In addition to measurement errors of the CPI, there is a problem of incongruence between the definition of inflation as a sustained and generalized increase of prices and the traditional measure associated with the CPI. We use data from 1991 to 2005 to estimate a complementary indicator for Venezuela, the highest inflation country in Latin America. Latent inflation is defined as that component of measured inflation that has no impact on real output in the long-run. This notion, consequently, is consistent with a vertical long-run Phillips curve and therefore it is grounded on economic theory. Latent inflation is constructed placing dynamic restrictions on a structural vector auto regression system. We find that latent inflation reflects more closely the generalized and sustained price increases most likely to be impacted by monetary policy. Our results are consistent with the identifying restrictions and with the theoretical definition of inflation
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